Process for producing color prints



Patented Sept. 15, 1936 UNITED, STATES PATENT OFFICE Friedrich Lierg, Dresden, Germany, assignor to Jasma A.-G., Zurich, Switzerland, a company of Switzerland No Drawing. Application August 14, 1930, Serial No. 475,372. In Great Britain September 12,

3 Claims.

Many of the processes for producing prints in natural colors make use of the fact that unhardened gelatin may readily be colored by means of dyestuffs whereas hardened gelatin cannot be I so colored atall, or only with difficulty. This fact is also utilized in the said processes in order to obtain paper prints in natural colors in a very simple manner by imprinting this imbibed dyestufi image on to gelatin printing paper. The

10 disadvantage of yielding only very impure whites which attends these printing processes was only removed when the hardened gelatin was used as a printing matrix, a relief of the tanned gelatin being prepared by dissolving out the unhardened l gelatin in warm water. But then the new difficulty arose of making the hardened gelatin, which is inherently dye-repelling, receptive for dyestuffs, which difficulty has not yet been obviated with complete satisfaction in every respect by the 20 methods heretofore known. All these printing processes based on the absorption or imbibition principle, however, entail two great disadvantages,

as a result of which their practical use is seriously impaired. In the first place the prints produced 25 by these known methods show imperfect image sharpness owing to the fact that the dyestufi proceeding from the gelatin printing image into the gelatin of the printing paper spreads into the latter, not only vertically, but laterally as well,

as which leads to blurred and indefinite contours,

and in the second place the absorption or imbibition prints, for reason hereinafter stated, show a gradation differing from that of the original image, which is a very serious disadvantage for the 35 production of three-color prints true to nature. For the purpose of avoiding the blurred contours of the image it has been proposed to use particularly hard, and therefore less absorptive, gelatin for the printing paper. This leads to a partial 4i) improvement but by no means to a removal of the blur of the print, and, moreover, it also strongly retards the printing speed and renders the use of printing presses essential for the production of uniform prints. It has also been 5 proposed to add to the print gelatin metallic compounds which are dye mordanting mediums such as are usual for fixing dyes in the fabric dyeing art. The addition of such metallic compounds acts pre-eminently so as to harden the gelatin 60 and consequently leads to a lessening of the strong lateral spreading of the dyestuffs; however, the positive and complete fixation of these dyestuffs by this formation of lakes, in which fixation, in the dyeing industry, the fibers them- 55 selves play an essential chemical role, could not be attained in photography, 1. e. in conjunction with gelatin. On the contrary, with the metal mordants used in the prior patent specifications referred to a subsequent fixation of the dye image by further chemical treatment baths and a coat- 5 ing of a layer of collodion for protection against the effects of moisture were found to be neces- Sary.

Up till now, the obviation has been unsuccessin] of the particularly disadvantageous falsification of the gradation of the print images, which on the one hand is to be attributed to the fact that the imbibed dyestuff is, to a large extent, washed out again from the finest and exceedingly thin, places of the gelatin relief during the necessary washing of the dyed print film before the squeegeeing, and on the other hand to the fact that, during the squeegeeing, the transference of the dyestuif from the printing film into the printing paper is not effected to completion but only to a certain equilibrium stage.

The essence of the present invention is first to fix transiently the dyestuif imbibed by the gelatin relief in a water-insoluble or difilcultly soluble form in the relief, so that during the washing away of the adhering dystufi solution no detail of the colored image is lost, and then to liberate the dyestuff again from the printing relief by a suitable chemical preparation of the printing paper, and to precipitate it instantly, completely and in a permanently water-insoluble form during the transference into the printing paper. All lateral spreading of the dyestuif in the gelatin is avoided by the careful and complete precipitation of the dyestuif during its entry into the gelatin and so that even when soft printing gelatin is used, an absoluteimage sharpness is produced. Above all, however, the transference of the dyestufi from the print relief into the printing paper is effected according to this invention not just 4 up to a certain equilibrium stage, but the dyestufi, in consequence of the strong chemical aflinity in combination with its complete precipitation, is drawn over into the printing paper completely and with extraordinary speed. It is only by this complete transference of the dyestufi image attained in this way in accordance with the process that the completely unchanged gradation of the print image can be produced; in the imbibition processes, known hitherto, transference of the dyestuff attainable only up to a certain equilibrium stage leads to a different printing of the halftones as compared with the color depths, and consequently to dull print images owing to the equalization of contrasts. Since, moreover, ac-

cording to the present in. ention the gelatin relief absorbs a quite definite amount of dyestuff up to saturation and this passes wholly into the printing paper owing to chemical combination, perfectly uniform color prints are always produced, which is now done for the first time and could not be attained by the usual imbibition processes, even by maintaining constant time of contact between the gelatin relief and the printing paper.

As fixing agents which precipitate the dyestuffs in the gelatin in such a thorough and permanently insoluble manner, as the present process requires and as is not possible by the common dyestufl fixing agents, are named barium salts for acid and particularly sulphonic acid dyestuffs. Preferably these are added to the layer of the printing paper in insoluble, finely divided form, e. g. as barium carbonate, and the printing relief, colored e. g. with diamine fast blue FF, brilliant pure blue Schultz 541 or pure diamine blue FF, carmoisine red, Schultz 163 is squeegeed on. The dyestuff, which enters into the printing paper, is there immediately precipitated as insoluble baryta salt owing to chemical interaction. If the gelatin relief of the part color component, which has been colored with carmoisine D Schultz 193, is squeeseed on to this blue image in accurate register therewith the red image mikado gold-colored Schultz 10 is produced. By transference of the yellow part colar image mimosa yellow Schultz 198 in an analogous manner a complete colored image of perfect sharpness is then obtained. If the printing is effected with basic dyestuffs, for instance red Schultz 569, auramine yellow Schultz 494 dyestuff-drawing mordant compounds e. g. cuprous iodide, silver iodide, copper thio-cyanate, may be added to the gelatin of the printing paper. These firmly hold the basic dyestuffs and prevent their lateral spreading, since they form a waterinsoluble addition compound with them. These addition-compounds (such as have been proposed already by An: in his British Patent No. 245,163) possess the drawback that they are non-transparent, so that they cannot be used for projectionpictures incolor, and they possess the further drawback that they do not precipitate the dyestufis in an insoluble manner, so that they pass into the baryto-layer when drying the paper image of the gelatin. According to the present invention these two drawbacks are avoided in that these dyestuif mordant images are bathed in sulphurated phenols known by the trade-name Katanol" or in dyestufi-precipitating complex acids such as phosphortungstic acid or phosphormolybdic acid .Od-IaJlMoO: and hereafter the mordant-members are fixed by hyposulphite of soda. The said dyestuif precipitating agents may also, according to the present invention, be introduced directly into the gelatin, since they form with this transparent, strongly dye-drawing compounds, so that the basic dyestuifs penetrating into the gelatin are precipitated instantly by these compounds as perfectly insoluble, transparent dyestufl. compounds.

When chemically preparing the printing paper and in order to promote the correct working thereof, the dyestuff imbibed in the gelatin printing relief is chemically combined with the same or temporarily transformed into an insoluble or difficultly soluble form.

When using acid dyestuffs, the free dye acids of which are insoluble, it issufiicient to introduce the colored relief into a weak acid bath without rinsing, whereupon the dyestufl in the relief is precipitated as dye acid.

The dye acid is precipitated fully water-insoluble by means of diluted hydrochloric acid for instance from the aqueous solution of brilliant pure blue.

The gelatin-free places can then be cleansed by washing with water without there being any fear of the slightest loss of the dyestuif absorbed by the gelatin. Before squeegeeing the relief prepared in this manner on to the printing paper the latter is bathed in a solution which converts the insoluble form of the dyestuif into a soluble form. In the case of dye acids, for example alkali baths such as diluted soda or borax solution are employed herefor.

When using basic dyestuffs for printing these are converted in an analogous manner, by bathing the gelatin relief in alkali, litO the insoluble color base, or else are converted into an insoluble compound which readily splits up when bathed e. g. in picric acid In the case of basic dyestuffs, however, the chemical activity of gelatin itself may also be employed for temporarily rendering the dyestuif in the gelatin relief insoluble, by specially choosing basic dyestuif for dyeing purposes having a chemical affinity towards albumin bodies which is so high that they enter into a more stable chemical combination with the gelatin itself, dyestuffs suited for this purpose being for instance crystal-violet Schultz 516 or fuchsine Schultz 512.

I claim:

1. Process for producing color prints by transferring a dyestuff from a printing matrix to an image ground, which consists in using the printing matrix in the form of a colloid relief, imbibing said relief with a. dyestufi, temporarily binding the imbibed dyestuif in a diflicultly soluble manner by treating said relief with compounds precipitating the dyestuff, placing in contact said relief with the image ground prepared with a chemical agent for releasing the dyestuif from said relief so that it may pass to the image ground and is precipitated in said image ground in a water-insoluble form.

2. Process for producing color prints by transferring a dyestuff from a printing matrix to an image ground, which consists in using the printingmatrix in the form of a colloid relief, imbibing said relief with a dyestufi of an aflinity for albuminous substances, temporarily binding the imbibed dyestuif in a difllcultly soluble manner by treating said relief with compounds precipitating the dyestuff, placing in contact said relief with the image ground prepared with a chemical 7 agent for releasing the dyestuif from said relief so that it may pass to the image ground and is precipitated in said image ground in a waterinsoluble form.

3. Process for producing color prints by transferring a dyestuif from a printing matrix to an image ground, which consists in using the printing matrix in the form of a colloid relief produced capable of binding a dyestuii' in a dimcultly soluble manner, imbibing said relief with a dyestufl of an aflinity for said substances, temporarily binding the imbibed dyestui! in a dimcultly soluble manner by treating said relief with compounds precipitating the dyestufl, placing in contact said relief with the image ground prepared with a' chemical agent for releasing the dyestuitfrom said relief so that it may pass to the image ground and is precipitated in said image. ground in a. water-insoluble form.

FRIEDRICH LIERG. 

